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Complex Topography (complex + topography)
Selected AbstractsDirect Microfabrication of Topographical and Chemical Cues for the Guided Growth of Neural Cell Networks on Polyamidoamine HydrogelsMACROMOLECULAR BIOSCIENCE, Issue 8 2010Gabriel Dos Reis Abstract Cell patterning is an important tool for organizing cells in surfaces and to reproduce in a simple way the tissue hierarchy and complexity of pluri-cellular life. The control of cell growth, proliferation and differentiation on solid surfaces is consequently important for prosthetics, biosensors, cell-based arrays, stem cell therapy and cell-based drug discovery concepts. We present a new electron beam lithography method for the direct and simultaneous fabrication of sub-micron topographical and chemical patterns, on a biocompatible and biodegradable PAA hydrogel. The localized e-beam modification of a hydrogel surface makes the pattern able to adsorb proteins in contrast with the anti-fouling surface. By also exploiting the selective attachment, growth and differentiation of PC12 cells, we fabricated a neural network of single cells connected by neuritis extending along microchannels. E-beam microlithography on PAA hydrogels opens up the opportunity of producing multifunctional microdevices incorporating complex topographies, allowing precise control of the growth and organization of individual cells. [source] Spatial patterns of simulated transpiration response to climate variability in a snow dominated mountain ecosystemHYDROLOGICAL PROCESSES, Issue 18 2008Lindsey Christensen Abstract Transpiration is an important component of soil water storage and stream-flow and is linked with ecosystem productivity, species distribution, and ecosystem health. In mountain environments, complex topography creates heterogeneity in key controls on transpiration as well as logistical challenges for collecting representative measurements. In these settings, ecosystem models can be used to account for variation in space and time of the dominant controls on transpiration and provide estimates of transpiration patterns and their sensitivity to climate variability and change. The Regional Hydro-Ecological Simulation System (RHESSys) model was used to assess elevational differences in sensitivity of transpiration rates to the spatiotemporal variability of climate variables across the Upper Merced River watershed, Yosemite Valley, California, USA. At the basin scale, predicted annual transpiration was lowest in driest and wettest years, and greatest in moderate precipitation years (R2 = 0·32 and 0·29, based on polynomial regression of maximum snow depth and annual precipitation, respectively). At finer spatial scales, responsiveness of transpiration rates to climate differed along an elevational gradient. Low elevations (1200,1800 m) showed little interannual variation in transpiration due to topographically controlled high soil moistures along the river corridor. Annual conifer stand transpiration at intermediate elevations (1800,2150 m) responded more strongly to precipitation, resulting in a unimodal relationship between transpiration and precipitation where highest transpiration occurred during moderate precipitation levels, regardless of annual air temperatures. Higher elevations (2150,2600 m) maintained this trend, but air temperature sensitivities were greater. At these elevations, snowfall provides enough moisture for growth, and increased temperatures influenced transpiration. Transpiration at the highest elevations (2600,4000 m) showed strong sensitivity to air temperature, little sensitivity to precipitation. Model results suggest elevational differences in vegetation water use and sensitivity to climate were significant and will likely play a key role in controlling responses and vulnerability of Sierra Nevada ecosystems to climate change. Copyright © 2008 John Wiley & Sons, Ltd. [source] A distributed approach for estimating catchment evapotranspiration: comparison of the combination equation and the complementary relationship approachesHYDROLOGICAL PROCESSES, Issue 8 2003Z. X. Xu Abstract In large river basins, there may be considerable variations in both climate and land use across the region. The evapotranspiration that occurs over a basin may be drastically different from one part of the region to another. The potential influence of these variations in evapotranspiration estimated for the catchment is weakened by using a spatially based distributed hydrological model in such a study. Areal evapotranspiration is estimated by means of approaches requiring only meteorological data: the combination equation (CE) model and the complementary relationship approach,the complementary relationship areal evapotranspiration (CRAE) and advection,aridity (AA) models. The capability of three models to estimate the evapotranspiration of catchments with complex topography and land-use classification is investigated, and the models are applied to two catchments with different characteristics and scales for several representative years. Daily, monthly, and annual evapotranspiration are estimated with different accuracy. The result shows that the modified CE model may underestimate the evapotranspiration in some cases. The CRAE and AA models seem to be two kinds of effective alternatives for estimating catchment evapotranspiration. Copyright © 2003 John Wiley & Sons, Ltd. [source] Solution of the 2-D shallow water equations with source terms in surface elevation splitting formINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 5 2007Dong-Jun Ma Abstract A vertex-centred finite-volume/finite-element method (FV/FEM) is developed for solving 2-D shallow water equations (SWEs) with source terms written in a surface elevation splitting form, which balances the flux gradients and source terms. The method is implemented on unstructured grids and the numerical scheme is based on a second-order MUSCL-like upwind Godunov FV discretization for inviscid fluxes and a classical Galerkin FE discretization for the viscous gradients and source terms. The main advantages are: (1) the discretization of SWE written in surface elevation splitting form satisfies the exact conservation property (,,-Property) naturally; (2) the simple centred-type discretization can be used for the source terms; (3) the method is suitable for both steady and unsteady shallow water problems; and (4) complex topography can be handled based on unstructured grids. The accuracy of the method was verified for both steady and unsteady problems, including discontinuous cases. The results indicate that the new method is accurate, simple, and robust. Copyright © 2007 John Wiley & Sons, Ltd. [source] Performance of finite volume solutions to the shallow water equations with shock-capturing schemesINTERNATIONAL JOURNAL FOR NUMERICAL METHODS IN FLUIDS, Issue 10 2002K. S. Erduran Abstract Numerical methods have become well established as tools for solving problems in hydraulic engineering. In recent years the finite volume method (FVM) with shock capturing capabilities has come to the fore because of its suitability for modelling a variety of types of flow; subcritical and supercritical; steady and unsteady; continuous and discontinuous and its ability to handle complex topography easily. This paper is an assessment and comparison of the performance of finite volume solutions to the shallow water equations with the Riemann solvers; the Osher, HLL, HLLC, flux difference splitting (Roe) and flux vector splitting. In this paper implementation of the FVM including the Riemann solvers, slope limiters and methods used for achieving second order accuracy are described explicitly step by step. The performance of the numerical methods has been investigated by applying them to a number of examples from the literature, providing both comparison of the schemes with each other and with published results. The assessment of each method is based on five criteria; ease of implementation, accuracy, applicability, numerical stability and simulation time. Finally, results, discussion, conclusions and recommendations for further work are presented. Copyright © 2002 John Wiley & Sons, Ltd. [source] Three-dimensional spatial interpolation of surface meteorological observations from high-resolution local networksMETEOROLOGICAL APPLICATIONS, Issue 3 2008Francesco Uboldi Abstract An objective analysis technique is applied to a local, high-resolution meteorological observation network in the presence of complex topography. The choice of optimal interpolation (OI) makes it possible to implement a standard spatial interpolation algorithm efficiently. At the same time OI constitutes a basis to develop, in perspective, a full multivariate data assimilation scheme. In the absence of a background model field, a simple and effective de-trending procedure is implemented. Three-dimensional correlation functions are used to account for the orographic distribution of observing stations. Minimum-scale correlation parameters are estimated by means of the integral data influence (IDI) field. Hourly analysis fields of temperature and relative humidity are routinely produced at the Regional Weather Service of Lombardia. The analysis maps show significant informational content even in the presence of strong gradients and infrequent meteorological situations. Quantitative evaluation of the analysis fields is performed by systematically computing their cross validation (CV) scores and by estimating the analysis bias. Further developments concern the implementation of an automatic quality control procedure and the improvement of error covariance estimation. Copyright © 2008 Royal Meteorological Society [source] The effects of basic flow and topography on the development of the sea breeze over a complex coastal environmentTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 605 2005Theodoros Nitis Abstract The aim of the present study is the analysis and evaluation of the influence of both the complex terrain and land-use on the formation of the sea breeze in a coastal environment. The Greater Rijeka Area, a region with complex topography and several islands, offers the opportunity to examine these relationships. According to the results, the MEMO model proved capable of simulating the mesoscale wind flow reasonably well. However, further investigation into the choice of some of the input model parameters and the parametrization employed was considered valuable as a means to improve model performance. For this reason, the influence of individual islands on the sea-breeze structure was investigated, and the model results for two different land-use databases were compared with the available measurements. The results indicated that the alteration of the model topography achieved by the removal of the islands from the Rijeka gulf had a significant impact on the simulated mesoscale circulation patterns, whereas the land surface heterogeneity had only a slight influence on the airflow. Copyright © 2005 Royal Meteorological Society [source] High-resolution limited-area ensemble predictions based on low-resolution targeted singular vectorsTHE QUARTERLY JOURNAL OF THE ROYAL METEOROLOGICAL SOCIETY, Issue 582 2002Inger-Lise Frogner Abstract The operational limited-area model, HIRLAM, at the Norwegian Meteorological Institute is used at 0.25° latitude/longitude resolution for ensemble weather prediction over Northern Europe and adjacent parts of the North Atlantic Ocean; this system is called LAMEPS. Initial and lateral boundary perturbations are taken from coarse-resolution European Centre for Medium-Range Weather Forecasts global ensemble members based on targeted singular vectors (TEPS). Five winter and five summer cases in 1997 consisting of 20 ensemble members plus one control forecast are integrated. Two sets of ensembles are generated, one for which both initial and lateral boundary conditions are perturbed, and another with only the initial fields perturbed. The LAMEPS results are compared to those of TEPS using the following measures: r.m.s. ensemble spread of 500 hPa geopotential height; r.m.s. ensemble spread of mean-sea-level pressure; Brier Skill Scores (BSS); Relative Operating Characteristic (ROC) curves; and cost/loss analyses. For forecasts longer than 12 hours, all measures show that perturbing the boundary fields is crucial for the performance of LAMEPS. For the winter cases TEPS has slightly larger ensemble spread than LAMEPS, but this is reversed for the summer cases. Results from BSS, ROC and cost/loss analyses show that LAMEPS performed considerably better than TEPS for precipitation, a result that is promising for forecasting extreme precipitation amounts. We believe this result to be linked to the high predictability of mesoscale flows controlled by complex topography. For two-metre temperature, however, TEPS frequently performed better than LAMEPS. Copyright © 2002 Royal Meteorological Society [source] Development and application of topographic descriptors for conditional analysis of rainfallATMOSPHERIC SCIENCE LETTERS, Issue 3 2009Emma Jayne Sakamoto Ferranti Abstract Upland rainfall is changing but regional climate models (RCMs) are poor at simulating observed precipitation in such areas of complex topography. This paper presents a method of examining observed rainfall patterns and processes under different conditions of synoptic meteorology and local topography. Objective topographic descriptors are defined and used to distinguish the modification of rainfall by local topography from that due to different synoptic conditions and climate change. A case study examining winter rainfall in Cumbria is presented. The conditional analysis method can be used to test RCM outputs so that model parameterisation can be improved. Copyright © 2009 Royal Meteorological Society [source] SPACE,TIME MODELLING OF SYDNEY HARBOUR WINDSAUSTRALIAN & NEW ZEALAND JOURNAL OF STATISTICS, Issue 1 2005Edward Cripps Summary This paper develops a space-time statistical model for local forecasting of surface-level wind fields in a coastal region with complex topography. The statistical model makes use of output from deterministic numerical weather prediction models which are able to produce forecasts of surface wind fields on a spatial grid. When predicting surface winds at observing stations, errors can arise due to sub-grid scale processes not adequately captured by the numerical weather prediction model, and the statistical model attempts to correct for these influences. In particular, it uses information from observing stations within the study region as well as topographic information to account for local bias. Bayesian methods for inference are used in the model, with computations carried out using Markov chain Monte Carlo algorithms. Empirical performance of the model is described, illustrating that a structured Bayesian approach to complicated space-time models of the type considered in this paper can be readily implemented and can lead to improvements in forecasting over traditional methods. [source] | |||||||||||||